Wafer stocker

ABSTRACT

A wafer stocker is capable of further improving an environment around wafers. The wafer stocker includes a housing, a loading device provided on a front surface of the housing, a wafer cassette shelf arranged in the housing, a wafer transfer robot configured to move the wafers from a transfer container mounted on the loading device to a wafer cassette in the wafer cassette shelf, a wafer cassette delivery device configured to move the wafer cassette in the wafer cassette shelf to a stage having a different height, and a fan filter unit configured to generate a laminar flow in a wafer transfer space and in a wafer cassette transfer space.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a national stage application of International PatentApplication PCT/JP2019/046033, filed on Nov. 25, 2019, which claimspriority to Japan Patent Application No. 2018-222883, filed on Nov. 23,2018, both of which are hereby incorporated by reference in theirentireties.

TECHNICAL FIELD

The present disclosure relates to a wafer stocker for temporary storageof wafers.

BACKGROUND

In a semiconductor device manufacturing process, wafers are processed ina clean room to improve the yield and quality. In order to properlymaintain the atmosphere around the wafers, a storage pod (transfercontainer) called a FOUP (Front-Opening Unified Pod) is used. A FOUPstocker that temporarily stores such a FOUP in a clean room has beenknown in the related art (see, e.g., Patent Document 1).

The FOUP stocker includes a plurality of shelves arranged in multiplestages in a height direction, and is configured so that FOUPsaccommodating unprocessed wafers therein and FOUPs accommodatingprocessed wafers therein can be placed on the shelves. In other words,the FOUP stocker is configured to place and store the entire FOUP (theentire FOUP accommodating the wafers) on the shelves in the FOUPstocker.

PRIOR ART DOCUMENT Patent Document

-   Patent Document 1: Japanese National Publication of International    Patent Application No. 2009-541599

As semiconductor devices are further miniaturized, it may be required tofurther improve the atmosphere around wafers even in the internal spaceof a stocker. Since a small amount of dust is present even in a cleanroom, the dust may adhere to the surface of a FOUP. Further, since theFOUP is generally made of a water-absorbent resin material, moisture inthe atmosphere in the clean room may be introduced into the FOUP. Ifsuch a FOUP is brought into the FOUP stocker described in PatentDocument 1, it may be difficult to maintain a good atmosphere in theFOUP stocker due to the dust or moisture released from the FOUP.Therefore, in the configuration in which the entire FOUP is stored inthe stocker as described in Patent Document 1, the improvement of theatmosphere around the wafers may be hindered even if the stocker isfilled with, for example, nitrogen or dry air.

The present disclosure provides embodiments of a wafer stocker capableof improving an atmosphere around wafers.

SUMMARY

According to one embodiment of the present disclosure, a wafer stockerincludes: a housing; a loading device installed on a front surface ofthe housing and configured to mount a transfer container capable ofaccommodating a plurality of wafers; a wafer cassette shelf arranged inthe housing and configured to store a plurality of wafer cassettes in amulti-stage manner, the wafer cassettes configured to store theplurality of wafers in a multi-stage manner; a wafer transfer robotconfigured to load and unload the wafers between the transfer containermounted on the loading device and the wafer cassettes stored in thewafer cassette shelf; a wafer cassette delivery device configured tomove the wafer cassettes stored in a predetermined stage among aplurality of stages of the wafer cassette shelf to a stage having atleast a height different from the predetermined stage; and a fan filterunit configured to generate a laminar flow in a wafer transfer space ofthe housing in which the wafer transfer robot is arranged and in a wafercassette transfer space of the housing in which the wafer cassettedelivery device is arranged.

The wafer stocker according to the present disclosure has aconfiguration in which the wafers are stored in units of the wafercassette capable of accommodating the wafers in multiple stages.Therefore, as compared with the stocker in the related art thataccommodates an entire transfer container such as a FOUP or the like, itis possible to prevent or suppress a situation in which the dustadhering to the outer surface of the transfer container enters thehousing and scatters or accumulates in the housing.

In addition, the wafer stocker according to the present invention has aconfiguration in which the wafers are stored generally through the useof the wafer cassette smaller than the transfer container. Therefore, ascompared with the stocker in the related art that accommodates thetransfer container, it is possible to downsize the entire stocker,increase the number of wafers to be stored, and narrow the footprint.Further, since the wafer stocker according to the present disclosure hasa configuration in which the wafer cassette is delivered in the housing,when the wafers are moved to different stages, it is possible to improvethe transfer efficiency as compared with the case where the wafers aremoved one by one.

Further, in the wafer stocker according to the present disclosure, thelaminar flow is generated by the fan filter unit in the wafer transferspace and the wafer cassette transfer space. Therefore, it is possibleto suppress the scattering of the dust generated during the operation ofthe wafer transfer robot or the operation of the wafer cassette deliverydevice.

Further, in the wafer stocker according to the present disclosure, thewafer transfer robot may be configured to deliver the wafers between thetransfer container mounted on the loading device and the wafer cassettearranged in a stage of a height facing the transfer container in afront-rear direction among the plurality of stages of the wafer cassetteshelf.

By doing so, it is possible to minimize the time required for deliveringthe wafers between the transfer container and the wafer cassette, and toshorten the takt time.

Further, in the wafer stocker according to the present disclosure, acirculation path for circulating a gas that includes the wafer transferspace and the wafer cassette transfer space may be formed in thehousing.

By doing so, for example, as compared with a configuration in which thegas is supplied into the housing and entirely discharged from thehousing, it is possible to reduce the amount of gas supplied, and toreduce the running cost.

According to the present disclosure, it is possible to provide a waferstocker capable of improving an atmosphere around wafers.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is an overall schematic view of a wafer stocker according to anembodiment of the present disclosure.

FIG. 2 is an exploded view of the wafer stocker shown in FIG. 1 .

FIG. 3 is an enlarged view of a part of FIG. 1

FIGS. 4A to 4D are schematic side views showing an operation flow of aloading device according to the embodiment.

FIG. 5 is a schematic side view of the wafer stocker showing a gascirculation path according to the embodiment.

FIG. 6 is a view showing an operation flow of the wafer stockeraccording to the embodiment corresponding to FIG. 1 .

FIG. 7 is a view showing an operation flow of the wafer stockeraccording to the embodiment corresponding to FIG. 1 .

FIG. 8 is a view showing an operation flow of the wafer stockeraccording to the embodiment corresponding to FIG. 1 .

FIG. 9 is a view showing an operation flow of the wafer stockeraccording to the embodiment corresponding to FIG. 1 .

FIG. 10 is an exploded view of a wafer stocker according to amodification.

FIG. 11 is an exploded view of a wafer stocker according to anothermodification.

DETAILED DESCRIPTION

Embodiments of the present disclosure will now be described in detailwith reference to the accompanying drawings.

A wafer stocker X (see FIG. 1 ) according to the present embodiment isprovided in a clean room used in a semiconductor manufacturing process.The wafer stocker X can temporarily store wafers, which are taken outfrom a transfer container capable of accommodating the wafers, inside ahousing 1 maintained in a high degree of cleanliness.

In the present embodiment, a FOUP 10 is used as a transfer container. Asshown in FIGS. 4A to 4D, the FOUP 10 includes a FOUP main body Y3(transfer container main body) having an internal space YS which isopenable through a loading/unloading port Y1 as an opening, and a FOUPdoor Y2 (transfer container door) capable of opening and closing theloading/unloading port Y1. The FOUP 10 is configured to accommodate aplurality of wafers in a multi-stage shape in a height direction H, sothat the wafers can be loaded and unloaded through the loading/unloadingport Y1. FIGS. 4A to 4D are schematic views showing an operation flowfor the FOUP 10, which follows the order of FIGS. 4A, 4B, 4C and 4D aswill be described later.

The FOUP main body Y3 includes a shelf portion (wafer mounting shelf)capable of mounting a plurality of wafers in multiple stages at apredetermined pitch in the internal space YS. As shown in FIG. 4A, aport Y4 is installed at a predetermined position on the bottom wall ofthe FOUP main body Y3. The port Y4 has, for example, a hollowcylindrical grommet seal fitted in a port mounting through-hole formedin the bottom wall of the FOUP main body Y3, and is configured to beopenable and closable by a check valve. A flange portion to be grippedby a container transfer device such as an OHT or the like is installedat the central portion of the upward surface of the upper wall of theFOUP main body Y3.

The FOUP door Y2 is a substantially plate-like member. The FOUP door Y2is arranged so as to face a loading device door 23 of a loading device 2in a state of being mounted on a mounting table 21 (described later) ofthe loading device 2. The FOUP door Y2 is provided with a latch key (notshown) for locking the FOUP door Y2 to the FOUP main body Y3. A gasketY5 is installed at a predetermined portion of the FOUP door Y2 thatcomes into contact with or is close to the FOUP main body Y3 in a statein which the loading/unloading port Y1 is closed by the FOUP door Y2.The FOUP door Y2 is configured so that the internal space YS of the FOUP10 can be sealed by bringing the gasket Y5 into contact with the FOUPmain body Y3 and elastically deforming the gasket Y5 (see FIGS. 4A and4C).

In the stocker of the related art that stores the entire FOUP 10therein, even if the atmosphere of the space where the FOUP 10 is storedis filled with nitrogen, dry air, or the like to achieve a higher degreeof cleanliness, dust or the like adhering to the surface of the FOUP 10in the clean room may be brought into the stocker and accumulatedtherein. Further, in general, the FOUP 10 is formed of a water-absorbentresin material (e.g., polycarbonate). Therefore, even if the internalspace of the stocker in the related art is filled with nitrogen, dryair, or the like, the moisture introduced into the FOUP 10 in the cleanroom is diffused in the stocker. This makes it difficult to control andkeep the humidity low in the internal space of the stocker. As describedabove, in the configuration in which the entire FOUP is stored in thestocker, it may be difficult to further improve the atmosphere aroundthe wafers. Therefore, in order to make it possible to further improvethe atmosphere around the wafers, the wafer stocker X of the presentembodiment is configured specifically as follows.

As shown in FIGS. 1 and 2 , the wafer stocker X according to the presentembodiment includes a housing 1, a loading device 2, a wafer cassetteshelf 3, a wafer transfer robot 4, and a wafer cassette delivery device5. The loading device 2 is arranged in close contact with a front wall11 of the housing 1 so as to form a part of the front wall 11 of thehousing 1. The loading device 2 includes a mounting table 21 on which awafer can be mounted. The wafer cassette shelf 3 is installed in thehousing 1 at a position spaced apart by a predetermined distancerearward from the front wall 11 of the housing 1, and is configured tostore a plurality of wafer cassettes C smaller than the FOUP 10 in amulti-stage manner (in other words, store the plurality of wafercassettes C in the height direction H). The wafer transfer robot 4performs a wafer loading/unloading process with respect to the FOUP 10on the mounting table 21 of the loading device 2. The wafer cassettedelivery device 5 moves the wafer cassette C stored in a stage of thewafer cassette shelf 3 to another stage having a different height (i.e.,the wafer cassette delivery device 5 moves the wafer cassette C in theheight direction H). The wafer cassette C is a well-known open cassettethat can store a plurality of wafers in a multi-stage manner (byarranging the wafers in the height direction H).

The housing 1 has a hollow rectangular parallelepiped shape, andincludes the front wall 11, a back wall 12, a ceiling wall 13, a floorbase 14, and a pair of left and right side walls (not shown) extendingforward from the vicinity of the left and right side edges of the backwall 12, respectively. The housing 1 can maintain an internal space 1Sthereof in a substantially sealed state and keep the internal space 1Sat a positive pressure (details will be described later). At apredetermined height position of the front wall 11, a housing windowportion 11 d penetrating in the front-rear direction D is formed. Thewafers can be taken in and out through the housing window portion 11 d.In the present embodiment, a plurality of housing window portions 11 d(three housing window portions 11 d in the illustrated example) isformed on the front wall 11 at a predetermined pitch along the widthdirection W. As shown in FIGS. 2 and 3 , an emergency off (EMO) button11 b and a monitor 11 c are installed on the front wall 11.

As shown in FIGS. 3 and 4A to 4D, the loading device 2 includes aplate-shaped standing base 22 arranged in an upright posture, a loadingdevice door 23 for opening and closing an opening 22 a formed in thestanding base 22, and a mounting table 21 provided on the standing base22 in a substantially horizontal posture. The loading device 2 isinstalled on the front surface of the housing 1. That is, the loadingdevice 2 is arranged so that the standing base 22 is brought into closecontact with the front wall 11 of the housing 1 from the front side ofthe housing 1. In this arrangement state, the opening 22 a formed in thestanding base 22 and the housing window portion 11 d formed in the frontwall 11 of the housing 1 overlap (communicate) with each other in thefront-rear direction D.

The mounting table 21 is installed on the upper portion of a horizontalbase 24 (support base) arranged to have a substantially horizontalposture at a position slightly above the center of the standing base 22in the height direction H. The mounting table 21 may support the FOUP 10in an orientation in which the FOUP door Y2 faces the loading devicedoor 23. Further, the mounting table 21 is configured to be movablebackward and forward with respect to the standing base 22. Specifically,the mounting table 21 is movable backward and forward between apredetermined docking position (see FIG. 4C) at which the FOUP door Y2adjoins the opening 22 a of the standing base 22 and a position (seeFIGS. 4A and 4B) at which the FOUP door Y2 is spaced apart by apredetermined distance more than the docking position from the standingbase 22. The mounting table 21 includes a plurality of protrusions(pins) (not shown) that protrude upward. By bringing these protrusionsinto engagement with holes (not shown) formed on the bottom surface ofthe FOUP 10, the FOUP 10 is positioned on the mounting table 21.Further, the mounting table 21 includes a lock claw (not shown) forfixing the FOUP 10. By hooking and fixing the lock claw to a lockedportion (not shown) formed on the bottom surface of the FOUP 10 to putit in a locked state, the FOUP 10 may be guided to and fixed at anappropriate position on the mounting table 21 in cooperation with thepositioning protrusions. Further, by releasing the locked state of thelock claw with respect to the locked portion formed on the bottomsurface of the FOUP 10, the FOUP 10 can be separated from the mountingtable 21.

The loading device door 23 includes a connecting mechanism 26 forconnecting the loading device door 23 and the FOUP door Y2, and isconfigured to be movable along a predetermined movement path whileholding the FOUP door Y2 with the connecting mechanism 26. Theconnecting mechanism 26 may be switched between a lid connection statein which the loading device door 23 and the FOUP door Y2 are connectedand a lid connection release state in which the connection of theloading device door 23 and the FOUP door Y2 is released. In the lidconnection state, the FOUP door Y2 can be removed from the FOUP mainbody Y3. In the lid connection release state, the FOUP door Y2 isattached to the FOUP main body Y3. The loading device door 23 isconfigured to be movable at least between a fully closed position (C)shown in FIG. 4A or the like and an open position (not shown). The fullyclosed position (C) is the position of the loading device door 23 whenthe internal space YS of the FOUP main body Y3 is sealed by the FOUPdoor Y2. The opening position is the position of the loading device door23 when the FOUP door Y2 is separated from the FOUP main body Y3 and theinternal space YS of the FOUP main body Y3 is opened toward the internalspace 1S of the housing 1. The loading device 2 may move the loadingdevice door 23 from the fully closed position to the open position whilemaintaining an upright posture of the loading device door 23, and mayfurther move the loading device door 23 downward from the open positionto a fully open position (0) shown in FIG. 4D while maintaining theupright posture. Such movement of the loading device door 23 isimplemented by a door moving mechanism 27 installed in the loadingdevice 2. In addition, the loading device 2 includes a movementrestricting portion (not shown) that restricts the movement of the FOUP10 on the mounting table 21 positioned at the docking position away fromthe standing base 22.

The loading device 2 includes a purging device P (see FIGS. 4A to 4D).The purging device P is configured to inject an inert gas such as anitrogen gas or the like or a purging gas such as dry air or the likeinto the internal space YS of the FOUP 10 to replace the atmosphere ofthe internal space YS of the FOUP 10 with the purging gas. The purgingdevice P may replace the atmosphere of the internal space YS of the FOUP10 with an inert gas of the same type as the inert gas supplied from thebelow-described gas introduction device 6 to the internal space 1S ofthe housing 1. The purging device P includes a plurality of purgingnozzles 2N (gas supply/discharge devices) which is arranged atpredetermined positions on the mounting table 21 while the upper endsthereof may be exposed. The purging nozzles 2N are attached toappropriate positions on the mounting table 21 according to thepositions of the ports Y4 formed on the bottom surface of the FOUP 10,and can be connected to the ports Y4. Using such a purging device P, thefollowing bottom purging process is performed. First, the purging deviceP causes some of the ports Y4 to function as “supply ports,” and injectsan appropriately-selected purging gas such as a nitrogen gas, an inertgas or dry air into the FOUP 10 via the purging nozzles 2N connected tothe supply ports. At the same time, the purging device P causes theremaining ports Y4 to function as “exhaust ports” and discharges the gasin the FOUP 10 via the purging nozzles 2N connected to the exhaustports. As a result, the FOUP 10 is filled with the purging gas.

The loading device 2 of the present embodiment includes a mapping part(not shown) capable of detecting the presence or absence and storageposture of a wafer in the FOUP 10.

A plurality of such loading devices 2 (three loading devices 2 in theillustrated example) is arranged side by side along the width directionW of the housing 1 on the front side of the housing 1.

As shown in FIGS. 1 and 2 , the wafer cassette shelf 3 includes a wafercassette shelf base 31 and a shelf main body 32 supported by the wafercassette shelf base 31. The shelf main body 32 is formed by integrallyassembling a plurality of shelf plates (not shown) arranged in astage-like manner and a shelf frame having side walls that can supportboth ends of each of the shelf plates. The wafer cassette shelf 3 of thepresent embodiment can store wafer cassettes C in 10 stages in theheight direction H. The lowermost mounting space of the wafer cassette C(first-stage mounting space) is set on an upper surface 31 a of thewafer cassette shelf base 31, and the second and higher wafer cassettesC from the bottom can be mounted on the shelf plates, respectively. Inthe present embodiment, the upper surface 31 a of the wafer cassetteshelf base 31 and the upper surface of the mounting table 21 of theloading device 2 are set at substantially the same height position.

The separation pitches of the wafer cassettes C stored in the wafercassette shelf 3 in a multiple-stage manner in the height direction Hmay be equal intervals. Alternatively, the separation pitches betweenthe shelves may be appropriately changed in consideration of, forexample, the arrangement locations of parts (e.g., beams (not shown) andthe like) that constitute the wafer cassette shelf 3. The wafer stockerX of the present embodiment is set so that the wafer cassettes C of thesame row number as the number of loading devices 2 can be placed on thewafer cassette shelf 3. That is, in the present embodiment, the wafercassette shelf 3 on which the wafer cassettes C can be placed in threerows in the width direction W is applied.

The wafer transfer robot 4 is installed between the front wall 11 of thehousing 1 and the wafer cassette shelf 3. The wafer transfer robot 4 canexecute a process of taking out a wafer from the FOUP 10 mounted on themounting table 21 of the loading device 2 and delivering the wafer tothe wafer cassette C stored in the wafer cassette shelf 3. Further, thewafer transfer robot 4 can execute a process of taking out a wafer fromthe wafer cassette C of the wafer cassette shelf 3 and putting the waferback into the FOUP 10. As shown in FIG. 2 , the wafer transfer robot 4includes, for example, an arm mechanism 42 in which wafer grippingportions (hands) are installed at the tips of a plurality of linkelements connected to each other so as to be horizontally swivel, and abase portion 43 configured to support the arm mechanism 42. The wafertransfer robot 4 has a link structure (articulated structure) in whichthe shape thereof is changed between a folded state in which the armlength of the arm mechanism 42 is minimized and an extended state inwhich the arm length is longer than in the folded state. A plurality ofindividually controllable wafer gripping portions may be installed atthe tip of the arm mechanism 42 in a multi-stage shape in the heightdirection H.

As shown in FIG. 5 , the space in the internal space 1S of the housing 1in which the wafer transfer robot 4 is installed is a space in front ofthe wafer cassette shelf 3 in the front-rear direction D and a space(wafer transfer space) functioning as a wafer transfer chamber 4S. Inthe present embodiment, as shown in FIG. 1 and the like, one wafertransfer robot 4 and one wafer aligner A are installed in the wafertransfer chamber 4S.

The wafer transfer robot 4 includes an exhaust box 44 that communicateswith the internal space of the base portion 43. Dust generated from adrive mechanism (drive mechanism of the arm mechanism 42) or the likeinstalled in the base portion 43 is forcibly collected in the exhaustbox 44 set to a negative pressure (see FIG. 5 ).

As shown in FIGS. 1 and 2 , the wafer cassette delivery device 5 isconfigured to move the wafer cassette C stored in the wafer cassetteshelf 3 to at least a stage having a different height in the wafercassette shelf 3. The wafer cassette delivery device 5 includes a wafercassette transfer arm 51 that can move in the front-rear direction D andthe height direction H, and a wafer cassette delivery device frame 52that supports the wafer cassette transfer arm 51. In the presentembodiment, the wafer cassette transfer arm 51 has a hand having abifurcated tip portion. However, the present disclosure is not limitedthereto. Further, the wafer cassette delivery device frame 52 has asubstantially rectangular parallelepiped shape, and includes a drivemechanism installed therein so as to move the wafer cassette transferarm 51 up and down and forward and backward. In the wafer cassettedelivery device 5, as shown in FIG. 2 , the same number of wafercassette transfer arms 51 as the number of rows of wafer cassettes C(three rows in the present embodiment) that can be placed on the wafercassette shelf 3 are arranged side by side in the width direction W.Further, the wafer cassette delivery device 5 is configured to deliverthe wafer cassette C of the row facing each wafer cassette transfer arm51 in the same row in the height direction H. As shown in FIG. 5 , aspace (wafer cassette transfer space) functioning as a wafer cassettetransfer chamber 5S that allows the wafer cassette C to move in theheight direction H is formed between the wafer cassette delivery deviceframe 52 and the wafer cassette shelf 3.

As shown in FIGS. 1, 2 and 5 , the wafer stocker X includes a gasintroduction device 6, an exhaust device 7, and a fan filter unit (FFU)8. The gas introduction device 6 supplies an inert gas into the housing1. The exhaust device 7 discharges the gas in the internal space 1S ofthe housing 1. The fan filter unit 8 passes the inert gas supplied fromthe gas introduction device 6 and generates a downward air flow (laminarflow) in the space (the space including the wafer cassette transferchamber 5S and the wafer transfer chamber 4S) extending from the wafercassette delivery device 5 to the front wall 11 of the housing 1.

The gas introduction device 6 includes a mass flow controller 61 (MFC)and a gas introduction pipe 62 (see FIG. 5 ). The mass flow controller61 is installed at a predetermined position in the housing 1 behind thewafer cassette delivery device 5 to control the flow rate whilemeasuring the mass flow rate of a fluid. The gas introduction pipe 62 isa pipe for supplying an inert gas (nitrogen gas in the presentembodiment) to the internal space 1S of the housing 1 via the mass flowcontroller 61. The gas introduction pipe 62 includes a gas introductionstart end pipe 63, a gas introduction vertical pipe 64, and a gasintroduction horizontal pipe 65. The gas introduction start end pipe 63is a pipe installed at a rear end portion of the housing 1 andcommunicating with a valve 61 v of the mass flow controller 61. The gasintroduction vertical pipe 64 extends from the front end (tip end) ofthe gas introduction start end pipe 63 to the vicinity of the ceilingwall 13 of the housing 1 along the inward surface of the back wall 12 ofthe housing 1. The gas introduction horizontal pipe 65 extends from theupper end of the gas introduction vertical pipe 64 to the vicinity ofthe front wall 11 of the housing 1 along the ceiling wall 13 of thehousing 1. The gas introduction horizontal pipe 65 has downwardly-openedholes (downward holes) formed at a predetermined pitch in the front-reardirection. As a result, the inert gas that reaches the gas introductionhorizontal pipe 65 from the valve 61 v of the mass flow controller 61via the gas introduction start end pipe 63 and the gas introductionvertical pipe 64 is supplied from the downward holes of the gasintroduction horizontal pipe 65 to the internal space 1S of the housing1 (see FIG. 5 ).

The fan filter unit 8 is a combination of a fan and a filter, andexhibits an air purifying function. In the wafer stocker X of thepresent embodiment, the fan filter unit 8 is arranged in a region thatextends from the upper end of the wafer cassette delivery device 5 (theupper end of the wafer cassette delivery device frame 52) to the inwardsurface of the front wall 11 of the housing 1. The inert gas supplied tothe internal space 1S of the housing 1 by the gas introduction device 6is sent to the wafer cassette transfer chamber 5S and the wafer transferchamber 4S as a highly clean down-flow (laminar flow) by the fan filterunit 8.

As shown in FIG. 5 , the exhaust device 7 includes an automatic pressurecontroller (APC) 71 and an exhaust port 72 communicating with a valve 71v of the automatic pressure controller 71. The automatic pressurecontroller 71 is installed in the housing 1 on the rear side of thewafer cassette delivery device 5 and on the lower side of the mass flowcontroller 61 of the gas introduction device 6. The gas in the down-flowgenerated by the fan filter unit 8 reaches the vicinity of the floorbase 14 of the housing 1 via the space between the wafer cassettedelivery device 5 and the front wall 11 of the housing 1, and flowstoward the exhaust port 72. A predetermined amount of gas is dischargedto the outside of the housing 1 via the exhaust port 72 and the valve 71v of the automatic pressure controller 71. In the present embodiment,passage paths 3T and 5T through which the air flow flowing toward theexhaust device 7 can pass are formed in the lower end portion of thewafer cassette shelf 3 and the lower end portion of the wafer cassettedelivery device 5, respectively (see FIGS. 2 and 5 ). Further, theexhaust device 7 includes an exhaust horizontal pipe 73 extending fromthe exhaust box 44 of the wafer transfer robot 4 toward the exhaust port72. The dust and the like collected in the exhaust box 44 of the wafertransfer robot 4 are discharged to the outside of the housing 1 via theexhaust horizontal pipe 73 and the exhaust port 72.

In the wafer stocker X of the present embodiment, a part of the gasflowing toward the exhaust device 7 is discharged, and most of theremaining gas is set to rise along the back wall 12 of the housing 1.Specifically, as shown in FIGS. 1, 2 and 5 , a pair of left and rightpartition walls 15 is installed and erected in the housing 1. A tubularspace TS as a return space for returning the gas to the fan filter unit8 is formed by the partition walls, the back wall of the wafer cassettedelivery device 5, and the back wall 12 of the housing 1. Further, ablower 9 is installed between the wafer cassette delivery device 5 andthe back wall 12 of the housing 1 and at a position higher than theexhaust port 72 of the exhaust device 7. The blower 9 generates a risingair flow in the tubular space TS. In the housing 1, the gas in therising air flow generated by the blower 9 joins the air flow flowingtoward the front wall 11 of the housing 1 when the gas reaches thevicinity of the ceiling wall 13 of the housing 1. Then, the gas passesthrough the fan filter unit 8 together with the inert gas supplieddownward from the gas introduction horizontal pipe 65 of the gasintroduction device 6, and flows along the air flow flowing downward. Asdescribed above, a gas circulation path for circulating most of theinert gas supplied from the gas introduction device 6 is formed in thehousing 1.

In the wafer stocker X having such a configuration, the inert gas iscirculated in the housing 1 to maintain the internal space 1S of thehousing 1 at a positive pressure, which makes it possible to prevent theatmosphere outside the housing 1 from entering the housing 1.Specifically, the automatic pressure controller 71 controls the flow ofthe gas so that the pressure in the entire gas circulation path becomesa positive pressure with respect to the atmosphere outside the housing1. More specifically, the pressure in the space (storage area) in whichthe wafer cassette C is stored is controlled so as to be, for example,10 to 300 Pa (gauge pressure). More preferably, the pressure in thestorage area is controlled to, for example, 10 to 100 Pa (gaugepressure), or a low positive pressure (a slightly positive pressure). Asa result, the space in which a large number of wafer cassettes C arestored and the space in which the wafers are transferred can be in ahighly clean space, and the wafer characteristics can be maintained byan atmosphere having a low oxygen concentration (e.g., 10 to 100 ppm)and a low humidity (e.g., dew point temperature of −50 degrees C. orless).

Next, the operation flow of the wafer stocker X according to the presentembodiment will be described with reference to FIGS. 4A to 4D and 6 to 9. In FIGS. 6 to 9 , the front wall 11 and the partition walls 15 of thehousing 1 are omitted for the sake of convenience of explanation.

First, the FOUP 10 is placed on the mounting table 21 of the loadingdevice 2 by a container transfer device such as an OHT or the like (seeFIG. 4A). At this time, for example, the positioning protrusion providedon the mounting table 21 fits into the positioning recess of the FOUP 10to bring the lock claw on the mounting table 21 into a locked state(locking process). In the present embodiment, the FOUP 10 can be mountedon each of the three mounting tables 21 of the loading devices 2arranged side by side in the width direction W. Further, a seatingsensor (not shown) that detects whether or not the FOUP 10 is mounted ata predetermined position on the mounting table 21 may be configured todetect that the FOUP 10 is mounted at a normal position on the mountingtable 21.

In the loading device 2 of the present embodiment, when the FOUP 10 isplaced at a predetermined normal position on the mounting table 21, itis detected that the bottom surface portion of the FOUP 10 presses thepressed portion of, for example, a pressure sensor installed on themounting table 21. With this as a trigger, all the purging nozzles 2Ninstalled on the mounting table 21 are moved to above the upper surfaceof the mounting table 21 and are connected to the respective ports Y4 ofthe FOUP 10. As a result, the respective ports Y4 are switched from theclosed state to the open state. Then, the loading device 2 performs aprocess (bottom purging process) of supplying a nitrogen gas, which isan inert gas, to the internal space YS of the FOUP 10 by the purgingdevice P and replacing the internal space YS of the FOUP 10 with thenitrogen gas (FIG. 4B). During the bottom purging process, the gas inthe FOUP 10 is discharged to the outside of the FOUP 10 via the purgingnozzles 2N connected to the ports Y4 that function as exhaust ports.FIG. 4B schematically shows the supply direction of the nitrogen gas andthe discharge direction of the gas in the FOUP 10 during the bottompurging process by arrows. By such a bottom purging process, the loadingdevice 2 reduces the water concentration and the oxygen concentration inthe FOUP 10 to predetermined values or less, respectively, and changesthe environment around the wafers in the FOUP 10 to a low humidityenvironment and a low oxygen environment.

After the locking process, the loading device 2 of the presentembodiment moves the mounting table 21 located at the position shown inFIG. 4B to the docking position shown in FIG. 4C (docking process).Next, the loading device 2 performs a process of holding and fixing atleast both sides of the FOUP 10 by using a movement restricting part(clamping process), and switches the connecting mechanism 26 to the lidconnecting state (lid connecting process). Further, the loading device 2executes a process (sealing release process) in which the sealed stateof the inside of the FOUP 10 is released by moving the FOUP door Y2together with the loading device door 23 to open the opening 22 a of thestanding base 22 and the loading/unloading port Y1 of the FOUP 10 (seeFIG. 4D). The loading device 2 may be configured to perform a mappingprocess by the mapping part during the process of moving the loadingdevice door 23 from the open position to the fully open position (0).Thus, it is possible to sequentially detect the presence or absence andthe storage posture of the wafers stored and arranged in the heightdirection H in the FOUP 10.

By executing the sealing release process, the internal space YS of theFOUP main body Y3 and the internal space 1S of the housing 1 are broughtinto communication with each other. Thereafter, the wafer transfer robot4 performs the following wafer transfer process based on the information(wafer position) detected in the mapping process. That is, the wafertransfer robot 4 transfers the wafer in the FOUP 10 to the wafercassette C stored in the wafer cassette shelf 3, and transfers the waferin the wafer cassette C to the FOUP 10.

In the wafer stocker X, the mounting space of the first stage of thewafer cassette shelf 3 (specifically, the upper surface 31 a of thewafer cassette shelf base 31) is set as a delivery position of the waferdelivered by the wafer transfer robot 4 with respect to the wafercassette C. Therefore, before the wafer transfer process (the process oftransferring the wafer in the FOUP 10 into the wafer cassette C), thewafer stocker X performs the following process. First, for example, asshown in FIG. 6 , when viewed from the front, the wafer cassette C isnot placed in the first stage of the left row of the wafer cassetteshelf 3 (idle state). In this state, the wafer stocker X delivers thewafer cassette C stored in the stage (the third stage in the illustratedexample) above the second stage in the same row to the first stage ofthe wafer cassette shelf 3 by the wafer cassette delivery device 5(wafer cassette delivery process) (see FIG. 7 ).

In FIG. 6 , the transfer path of the wafer cassette C transferred by thewafer cassette transfer arm 51 is schematically indicated by an arrow.

As shown in FIG. 7 , the wafer stocker X performs the following “nextuse wafer cassette delivery process” during the wafer transfer processin which the wafer is delivered between the wafer cassette C set in thefirst stage of the wafer cassette shelf 3 and the FOUP 10. That is, thewafer stocker X delivers the wafer cassette C to be used in the nextwafer processing to the idle space in the first-stage mounting space ofthe wafer cassette shelf 3 by the wafer cassette delivery device 5. FIG.7 shows a state in which the wafer cassette C stored in the stage (thethird stage in the illustrated example) above the second stage of thecentral row of the wafer cassette shelf 3 is delivered to the center ofthe first-stage mounting space of the wafer cassette shelf 3 as a “nextuse wafer cassette.” In FIGS. 7 to 9 , the transfer path of the wafercassette C transferred by the wafer cassette transfer arm 51 isschematically shown by relatively thick arrows, and the transfer path ofthe wafer transferred by the wafer transfer robot 4 is schematicallyshown by relatively thin arrows. The wafer transfer robot 4 delivers thewafer between the FOUP 10 mounted on the loading device 2 and the wafercassette C arranged in the stage of a height facing the transfercontainer in the front-rear direction among the plurality of stages ofthe wafer cassette shelf 3.

The wafer stocker X performs the following sealing process on the FOUP10 for which the wafer transfer process has been completed. First, thewafer stocker X moves the loading device door 23 to the fully closedposition (C) by the door moving mechanism 27 of the loading device 2,and closes the opening 22 a of the standing base 22 and theloading/unloading port Y1 of the FOUP 10. Subsequently, the loadingdevice 2 executes a process of switching the connecting mechanism 26from the lid connection state to the lid connection release state (lidconnection release process). By this process, the internal space YS ofthe FOUP 10 is brought into a sealed state.

Subsequently, the loading device 2 performs a clamp release process ofreleasing the fixed state (clamped state) of the FOUP 10 kept by themovement restricting part. Next, the loading device 2 executes a processof moving the mounting table 21 away from the standing base 22 (dockingrelease process), and then releases the state in which the FOUP 10 islocked by the lock claw on the mounting table 21 (unlock process). As aresult, the FOUP 10 is delivered from the mounting table 21 of eachloading device 2 to the container transfer device, and is carried to,for example, the mounting table of the load port constituting the EFEM(Equipment Front End Module).

On the other hand, the wafer cassette C subjected to the wafer transferprocess is delivered from the first-stage mounting space of the wafercassette shelf 3 to the original-stage mounting space by the wafercassette delivery device 5 at an appropriate timing after the sealingprocess is performed by the loading device 2 (wafer cassette returnprocess). As shown in FIG. 8 , the wafer cassette return process can beexecuted during the wafer transfer process performed by using anotherwafer cassette C different from the target of the wafer cassette returnprocess.

As described above, the wafer stocker X can repeatedly perform the wafertransfer process as needed in a state in which a large number of wafercassettes C accommodating wafers in multiple stages or a large number ofwafer cassettes C not accommodating wafers are stored in the housing 1.FIG. 9 shows a state in which the FOUP 10 on the loading device 2 iscarried out from the state shown in FIG. 8 to the next process, and thewafer cassette C for which the wafer transfer process has been completedis returned from the first-stage mounting space of the wafer cassetteshelf 3 to the original-stage mounting space.

The wafer transfer process using the wafer transfer robot 4 is either aprocess of delivering the wafer in the FOUP 10 to the wafer cassette Cof the wafer cassette shelf 3, or a process of delivering the waferstored in the wafer cassette C into the FOUP 10. The process to beperformed may be appropriately selected. Further, the wafer in the FOUP10 may be delivered to the wafer cassette C via the wafer aligner Ainstalled in the wafer transfer chamber 4S, or the wafer of the wafercassette C may be delivered into the FOUP 10 via the wafer aligner A(see FIGS. 7 and 8 ). The operation of the wafer stocker X is controlledby a controller (not shown).

As described above, according to the wafer stocker X of the presentembodiment, the inert gas can be supplied into the housing 1 by the gasintroduction device 6, and the plurality of wafer cassettes C can bestored in a multi-stage manner in the positive-pressure housing 1 keptin a low oxygen concentration and a low water concentration andmaintained in a high degree of cleanliness. As a result, the entry ofthe atmosphere from the outside can be prevented, and the outgas or thelike generated from the wafer after the semiconductor processing processcan be blown down by the down-flow generated by the fan filter unit 8and can be discharged to the outside of the housing 1 by the exhaustdevice 7. In particular, since the wafer stocker X can store a largenumber of wafers, it is difficult to supply the entire amount of theinert gas from the outside in order to form a laminar flow. Therefore,it is effective to suppress the increase in running cost by forming thecirculation path of the inert gas in the internal space 1S of thehousing 1.

Further, the wafer stocker X according to the present embodiment has aconfiguration in which the wafers are stored in units of wafer cassettesC capable of accommodating the wafers in multiple stages. Therefore, ascompared with the FOUP stocker in the related art that accommodates theentire FOUP 10 therein, it is possible to prevent the dust adhering tothe outer surface of the FOUP 10 and the moisture introduced onto theouter surface of the FOUP from being released inside the stocker.Accordingly, it is possible to suppress a decrease in the degree ofcleanliness inside the stocker. Furthermore, with such a configuration,it is possible to prevent or suppress a situation in which outgas or thelike generated from the wafer after the semiconductor processing processenters and scatters in the stocker. As a result, it is possible toprevent or suppress a situation in which the wafer is contaminated inthe housing 1 of the wafer stocker X or in the internal space YS of theFOUP 10 communicating with the internal space 1S of the housing 1. Thatis, according to the wafer stocker X of the present embodiment, it ispossible to always maintain a high degree of cleanliness around thewafers and to prevent or suppress a situation in which particles andmoisture adhere to the wafer surface. Accordingly, it is possible tofurther improve the atmosphere around the wafers in the stocker.

Further, the wafer stocker X of the present embodiment has aconfiguration in which the wafer is generally stored using the wafercassette C smaller than the FOUP 10. Therefore, as compared with thestocker in the related art that accommodates the FOUP therein, it ispossible to reduce the size of the wafer stocker X as a whole and toreduce the footprint of the wafer stocker X. Alternatively, as comparedwith the stocker in the related art that accommodates the entire FOUPtherein, it is possible to increase the number of wafers that can beaccommodated in the wafer stocker X, while suppressing the increase inthe size of the entire apparatus. Moreover, the wafer stocker Xaccording to the present embodiment has a configuration in which thewafer cassette C stored in the wafer cassette shelf 3 is deliveredinside the housing 1. Therefore, as compared with the stocker in therelated art in which the entire FOUP is delivered in the housing, thedelivery space in the housing can be made compact.

Further, the wafer stocker X is configured so that the wafer cassettes Ccan be stored in a plurality of rows along the width direction W in thewafer cassette shelf 3, and includes the loading devices 2 and the wafercassette transfer arms 51 corresponding to the number of rows.Therefore, it is possible to efficiently perform the delivery process ofthe wafer cassette C and the wafer transfer process.

Further, among the wafer cassettes C stored in the wafer cassette shelf3, the wafer cassette C arranged at the height position facing the FOUP10 mounted on the mounting table 21 of the loading device 2 in thefront-rear direction D (specifically, the wafer cassette C mounted inthe first-stage mounting space) is set to the wafer cassette C to whichthe wafer is delivered by the wafer transfer robot 4. That is, the wafertransfer robot 4 delivers the wafer between the FOUP 10 mounted on theloading device and the wafer cassette C arranged in the stage of aheight facing the FOUP 10 in the front-rear direction among theplurality of stages of the wafer cassette shelf 3. Therefore, ascompared with a configuration in which the wafer is delivered by thewafer transfer robot 4 from the FOUP 10 to the wafer cassette C at aheight position not facing the FOUP 10 mounted on the mounting table 21of the loading device 2 in the front-rear direction D among the wafercassettes C stored in the wafer cassette shelf 3, for example, theheight of the delivery position of the wafer delivered by the wafertransfer robot 4 can be limited to a predetermined range. Accordingly,it is possible to shorten the takt time of the wafer transfer robot 4that transfers the wafer between the FOUP 10 and the wafer cassette C.

As a specific storage form of the wafer cassette C in the wafer cassetteshelf 3 of the wafer stocker X, there may be a form in which the wafercassette C accommodating frequently used wafers is stored in a mountingspace closer to the first-stage mounting space. As a result, it ispossible to shorten the access time for the wafers which are expected tobe used preferentially. In addition, the wafers with a relatively highdegree of pollution (the wafers that generate a large amount of outgas)are set to be stored in the mounting space of the stage below the waferswith a relatively low degree of pollution, which makes it possible tosuppress spreading of pollution. Further, the wafer degassed bylong-term storage in the housing may be moved to the upper stage.

According to the wafer stocker X of the present embodiment, it ispossible to partition the storage locations in the wafer cassette shelf3 depending on the type and state of the wafer, the semiconductorprocessing process applied to the wafer, and the like. Appropriatepartitions may be installed in the wafer cassette shelf 3 to define thepartition range.

Furthermore, in the present embodiment, the loading device 2 of thewafer stocker X has the same or similar configuration as the load portthat constitutes the EFEM, which makes it possible to save the labor andtime in designing and manufacturing a new loading device.

Although the embodiment of the present disclosure has been describedabove, the present disclosure is not limited to the configuration of theabove-described embodiment. For example, it may be possible toappropriately change the number of stages of the wafer cassette shelf(the number of mounting spaces of the wafer cassette in the heightdirection) and the number of rows of the wafer cassette shelf (thenumber of mounting spaces of the wafer cassette in the width direction).

As the wafer cassette delivery device, it may be possible to use adevice provided with a wafer cassette transfer arm that can move in thewidth direction of the housing in addition to moving up and down. Withsuch a wafer cassette delivery device, the wafer cassettes stored in thewafer cassette shelf can be moved to different rows by the wafercassette transfer arm.

Further, as the wafer cassette shelf, it may be possible to use a rotaryshelf that rotates in a horizontal plane. In this case, for example, aplurality of wafer cassette mounting spaces (e.g., four wafer cassettemounting spaces at a 90-degree pitch) may be provided at a predeterminedangle pitch in the circumferential direction orthogonal to the heightdirection H. Then, the wafer cassette mounted in each of the wafercassette mounting spaces may be configured to take a rotation angleposture facing the wafer transfer robot or the wafer cassette transferarm. In this way, the wafer transfer robot or the wafer transfer arm maybe allowed to access the wafer cassette mounting spaces. By doing so, itis possible to efficiently perform the wafer transfer process and thewafer cassette delivery process.

Furthermore, as the wafer cassette stored in the wafer cassette shelf,it may also be possible to use a wafer cassette that can be accessedfrom a total of four directions, i.e., one side and the other side inthe width direction W and one side and the other side in the front-reardirection D.

The wafer cassette delivery device may be capable of storing the wafercassettes in a plurality of stages along the height direction of onerow.

Further, the wafer cassette mounted in the mounting space of the stageother than the first stage of the wafer cassette shelf may be configuredto be located at a height position facing the transfer container mountedon the loading device in the front-rear direction. In such aconfiguration, it may also be possible to set the wafer cassette locatedat the height position as the “wafer cassette to be delivered by thewafer transfer robot.” That is, the wafer stocker of the presentdisclosure also has a configuration in which the wafer cassette placedin the second or higher stage is set as the “wafer cassette to bedelivered by the wafer transfer robot.”

In the above-described embodiment, the FOUP is adopted as the transfercontainer. However, in the present disclosure, it may also be possibleto use a transfer container other than the FOUP such as a MAC (MultiApplication Carrier), an H-MAC (Horizontal-MAC), an FOSB (Front OpenShipping Box), or the like.

Further, as the container transfer device, it may be possible to use anappropriate transfer device other than the OHT. It may also be possibleto use an OHS (Over Head Shuttle), an RGV (Rail Guided Vehicle), an AGV(Automated Guided Vehicle), and the like. The RGV and the AGV arecontainer transfer devices that run on the floor side in a factory. Whenthe container transfer device is the RGV, a rail (track) is installed onthe floor of a factory or the like.

Further, the wafer transfer robot may have a traveling shaft capable oftraveling in the width direction of the housing (parallel direction ofthe loading device). For example, when the number of rows of loadingdevices arranged side by side in the width direction of the housing islarge, it is preferable to use a wafer transfer robot having a travelingaxis extending in the width direction of the housing.

In the above-described embodiment, the nitrogen gas is taken as anexample of the inert gas supplied to the inside of the housing. However,the present disclosure not limited thereto. It may be possible to use adry gas, an argon gas, or the like. Similarly, the inert gas used forthe bottom purging process is not limited to the nitrogen gas.Alternatively, the gas supplied to the inside of the housing does notnecessarily have to be an inert gas, and may be, for example, dry air.According to this, it is possible to realize a low-humidity environmentwhich is not an environment having a low oxygen concentration.

Further, the container door (FOUP door) may be temporarily in aninclined posture (accompanied by an operation of drawing a partialarc-shaped trajectory) in the process of moving from the fully closedposition to the fully open position.

If the wafer alignment process may be omitted, the cost can be reducedby adopting a configuration in which the wafer aligner is not providedin the wafer transfer space.

Further, the gas introduction device may be configured by using anappropriate device other than the mass flow controller (MFC) thatcontrols the flow rate while measuring the mass flow rate of the fluid.Moreover, the gas exhaust device may be configured by using anappropriate device other than the automatic pressure controller (APC)that maintains the internal positive pressure according to the amount ofexhaust gas. For example, it may be possible to adopt a configuration inwhich the inert gas is introduced by a return duct that constitutes agas circulation path. If the inert gas is introduced by the return duct,a backflow may be generated in the housing when the flow rate is large.Therefore, by introducing the inert gas into the housing from a positionhigher than the fan filter unit, it is possible to cope with the problemof backflow. In addition, by introducing the inert gas into the housingfrom a position higher than the fan filter unit, the air pressure islocally increased at the position higher than the fan filter unit,whereby the laminar flow is not disturbed.

A gas circulation path does not necessarily have to be formed in thehousing. That is, the wafer stocker may be configured so that the gas isnot circulated and the gas supplied into the housing by the gasintroduction device is entirely discharged by the exhaust device.

The number of wafers that can be accommodated per wafer cassette is, forexample, 25, but it may also be possible to use a wafer cassette thatcan accommodate a number of wafers other than 25 in a multi-stagemanner.

A chemical filter may be installed around the return duct and theblower. Further, the return duct may be installed on a side surface ofthe housing.

In the wafer stocker, the fan filter unit is configured to generate adown-flow as a laminar flow. However, the present disclosure is notlimited thereto. The wafer stocker may be configured to generate alaminar flow flowing in the horizontal direction in, for example, thewafer transfer space and the wafer cassette transfer space.

As the loading device, it may be possible to use a dedicated loadingdevice different from the load port used in an EFEM.

It may also be possible to use the wafer stocker according to thepresent disclosure as a sorter. In this case, it is preferable toinstall a wafer front/back reversing machine together with a waferaligner in the wafer transfer space.

It may be possible to adopt a configuration in which the wafers arestored in the housing without having to use a wafer cassette, or aconfiguration in which the hands of the wafer transfer device hold andtransfer a plurality of wafers at the same time. Further, by allowingthe wafer transfer robot to be provided with a vertical movementmechanism, it may be possible for the wafer transfer robot to accesseach shelf and replace the wafers. Specifically, as shown in FIG. 10 ,the transfer system 1 a may include a moving mechanism 80. For example,the moving mechanism 80 may include a pair of columnar members 81erected on the front side and both left and right sides of the wafercassette shelf 3, and a floor member 82 arranged substantiallyhorizontally so as to be movable up and down along the columnar member81 by a motor (not shown) or the like. The wafer transfer robot 4, thewafer aligner A, and a buffer stocker 83 capable of temporarily storinga plurality of wafers may be arranged on the floor member 82. The wafertransfer robot 4 may move the wafer between the FOUP 10 and the bufferstocker 83, and further move the wafer between the buffer stocker 83 andthe wafer cassette shelf 3. The transfer system 1 a may not include thewafer cassette delivery device 5 (see FIG. 2 ), and instead may includea vertical plate 91 formed with a passage 92 through which gas can pass.A fan filter unit 84 that generates a down-flow (laminar flow) may beattached to the floor member 82. As a result, for example, it ispossible to suppress the scattering of the dust generated as the floormember 82 moves up and down.

Further, as a further modification of the transfer system 1 a, as shownin FIG. 11 , in a transfer system 1 b, the wafer transfer robot 4, themoving mechanism 80 and the like may be additionally installed on therear side of the wafer cassette shelf 3.

In addition, the specific configuration of each part is not limited tothe above embodiments, and various modifications may be made withoutdeparting from the scope of the present disclosure.

EXPLANATION OF REFERENCE NUMERALS

1: housing, 2: loading device, 3: wafer cassette shelf, 4: wafertransfer robot, 4S: wafer transfer chamber (wafer transfer space), 5:wafer cassette delivery device, 5S: wafer cassette transfer chamber(wafer cassette transfer space), 8: fan filter unit, 10: FOUP (transfercontainer), X: wafer stocker

What is claimed is:
 1. A wafer stocker, comprising: a housing includinga front wall and a back wall; a loading device installed on a frontsurface of the housing and configured to mount a transfer containercapable of accommodating a plurality of wafers; a wafer cassette shelfarranged in the housing and configured to store a plurality of wafercassettes in a multi-stage manner, the plurality of wafer cassettesconfigured to store the plurality of wafers in a multi-stage manner; awafer transfer robot configured to load and unload the wafers betweenthe transfer container mounted on the loading device and the wafercassettes stored in the wafer cassette shelf; a wafer cassette deliverydevice configured to move a wafer cassette stored in a predeterminedstage among a plurality of stages of the wafer cassette shelf to a stagehaving at least a height different from the predetermined stage; a fanfilter unit installed in the housing and configured to generate alaminar flow in a wafer transfer space of the housing in which the wafertransfer robot is arranged and in a wafer cassette transfer space of thehousing in which the wafer cassette delivery device is arranged; a gasintroduction pipe that extends horizontally along and under a ceilingwall of the housing in an internal space of the housing above the fanfilter unit and has a plurality of holes that are formed along anextending direction of the gas introduction pipe and configured tosupply gas to the fan filter unit; a return space installed in thehousing between the back wall and the wafer cassette delivery device;and a blower installed in the return space and configured to generate arising air flow that flows in the return space toward the fan filterunit, wherein a circulation path for circulating gas is formed in thehousing, the circulation path including the wafer transfer space, thewafer cassette transfer space, and the return space.
 2. The waferstocker of claim 1, wherein the wafer transfer robot is configured todeliver the wafers between the transfer container mounted on the loadingdevice and the wafer cassette arranged in a stage having a height facingthe transfer container in a front-rear direction among the plurality ofstages of the wafer cassette shelf.
 3. The wafer stocker of claim 1,further comprising a wafer aligner installed in the wafer transferspace, wherein the wafers are loaded and unloaded between the transfercontainer and the wafer cassettes via the wafer aligner.
 4. The waferstocker of claim 1, wherein the wafer transfer robot includes an exhaustbox configured to collect dust generated from the wafer transfer robotand connected to an exhaust device, and wherein the exhaust device isconfigured to discharge the dust collected in the exhaust box to anoutside of the housing.
 5. A wafer stocker, comprising: a housingincluding a front wall where a housing window is formed and a back wall;a loading device installed on a front surface of the front wall, havingan opening formed to communicate with the housing window and configuredto mount a transfer container to adjoin the transfer container to theopening, the transfer container being capable of accommodating aplurality of wafers; a wafer cassette shelf arranged in the housing andconfigured to store a plurality of wafer cassettes in a multi-stagemanner, the plurality of wafer cassettes configured to store theplurality of wafers in a multi-stage manner; a wafer transfer robotconfigured to load and unload the wafers between the transfer containermounted on the loading device and the wafer cassettes stored in thewafer cassette shelf through the housing window; a wafer cassettedelivery device configured to move a wafer cassette stored in apredetermined stage among a plurality of stages of the wafer cassetteshelf to a stage having at least a height different from thepredetermined stage; a fan filter unit configured to generate a laminarflow in a wafer transfer space of the housing in which the wafertransfer robot is arranged and in a wafer cassette transfer space of thehousing in which the wafer cassette delivery device is arranged; a gasintroduction pipe that extends horizontally along and under a ceilingwall of the housing in an internal space of the housing above the fanfilter unit and has a plurality of holes that are formed along anextending direction of the gas introduction pipe and configured tosupply gas to the fan filter unit; a return space installed in thehousing between the back wall and the wafer cassette delivery device;and a blower installed in the return space and configured to generate arising air flow that flows in the return space toward the fan filterunit, wherein a circulation path for circulating gas is formed in thehousing, the circulation path including the wafer transfer space, thewafer cassette transfer space, and the return space.
 6. The waferstocker of claim 5, further comprising a wafer aligner installed in thewafer transfer space, wherein the wafers are loaded and unloaded betweenthe transfer container and the wafer cassettes via the wafer aligner. 7.The wafer stocker of claim 5, wherein the wafer transfer robot includesan exhaust box configured to collect dust generated from the wafertransfer robot and connected to an exhaust device, and wherein theexhaust device is configured to discharge the dust collected in theexhaust box to an outside of the housing.
 8. The wafer stocker of claim5, wherein the wafer transfer robot is configured to deliver the wafersbetween the transfer container mounted on the loading device and thewafer cassette arranged in a stage having a height facing the transfercontainer in a front-rear direction among the plurality of stages of thewafer cassette shelf.